Ferguson, of Christchurch, overhauled the early leader, Australian Belinda Granger, in the final few hundred metres of the marathon to gain third place (8hr 57min 18sec) behind defending champion Yvonne van Vlerken, of the Netherlands (8hr 45min 48sec) and Hungarian Erika Csomor. (8hr 47min 5sec).
Speaking after the race, Ferguson said the conditions were so cold on the bike she did not know whether she would be able to finish.
Wanaka rookie professional Greenwood (31) acquitted herself well in the competitive field, finishing 15th in a personal best time of 9hr 52min 22sec.
Greenwood's coach, Val Burke, of Wanaka, said yesterday her charge had hit every goal she set herself to achieve in her first finish in under 10 hours.
Burke took over Greenwood's training regime from high-performance coach Mark Elliott earlier this year and "tweaked" the programme to improve her bike and run performance.
The courses in Roth and Wanaka were quite different but Greenwood had managed to carve 40min from her previous best 180km bike time and 8min off her previous best marathon time, as well as reducing her swim time.
Challenge Wanaka event director Victoria Murray-Orr said yesterday she had been in contact with Greenwood and she was "over the moon" with her result.
Auckland's Keiran Doe was among the early leaders in the men's race, along with defending champion and reigning world Ironman champion Chris McCormack, but both pulled out during the cycle.
Patrick Vernay, of France, won the race in 8hr 9min 47sec.
